kdb: Fix a potential buffer overflow in kdb_local()

[ Upstream commit 4f41d30cd6dc865c3cbc1a852372321eba6d4e4c ]

When appending "[defcmd]" to 'kdb_prompt_str', the size of the string
already in the buffer should be taken into account.

An option could be to switch from strncat() to strlcat() which does the
correct test to avoid such an overflow.

However, this actually looks as dead code, because 'defcmd_in_progress'
can't be true here.
See a more detailed explanation at [1].

[1]: https://lore.kernel.org/all/CAD=FV=WSh7wKN7Yp-3wWiDgX4E3isQ8uh0LCzTmd1v9Cg9j+nQ@mail.gmail.com/

Fixes: 5d5314d6795f ("kdb: core for kgdb back end (1 of 2)")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index ead4da947127075e825c9085ff20d69a23046dd4..23723c5727aacdcc24555364d61a56d70aace92e 100644 (file)
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -1350,8 +1350,6 @@ do_full_getstr:
                /* PROMPT can only be set if we have MEM_READ permission. */
                snprintf(kdb_prompt_str, CMD_BUFLEN, kdbgetenv("PROMPT"),
                         raw_smp_processor_id());
-               if (defcmd_in_progress)
-                       strncat(kdb_prompt_str, "[defcmd]", CMD_BUFLEN);
 
                /*
                 * Fetch command from keyboard